Abstract
This paper provides causal evidence that the sex composition of dating markets affects maternal and neonatal health. Using a novel instrument that leverages randomness in sex at birth to vary the availability of male partners, I find that a more favorable dating market for women decreases non-marital but increases marital fertility, lowers rates of chlamydia and hypertension among mothers, and decreases the incidence of low APGAR scores and a composite index of adverse birth outcomes. These effects appear to operate primarily through changes in relationship dynamics and selection into motherhood. Connecting this to inequalities, racial disparities in partner availability can explain 5–10% of the Black–White pregnancy health gap.